People will be allowed to travel to see their loved ones tonight.

The prime minister stress that Christmas would be different this year and he warned that families would need to make a personal judgment about visiting elderly relatives on the vulnerable.

This is what has been agreed across the UK Up to three households will be able to mix in each other's homes.

But you can't go to pubs or restaurants.

You will be allowed to travel to see family on.

You can go anywhere in the UK The new rules covered just five days from the 23rd to the 27th off December.

Here's our deputy political editor Vicky Young.

Preparations are underway across all four nations of the United Kingdom for a Christmas that won't be like any other Coronavirus means that for months we've all had to live with regulations telling us who we concede on where for a few days the rules will be relaxed.

This year, Christmas will be different.

Many of us are longing to spend time with family and friends, irrespective of our faith or background.

And yet we can't afford to throw caution to the wind.

The virus doesn't know it's Christmas, and we must all be careful.

Many will welcome the move.

But what about places like where there's being a spike in coronavirus cases in recent days?

Well, I think I rather it didn't happen because I think we need to be.

If we get keep safe now, hopefully New Year, we can move forward.

I think it's inevitable because people would do it regardless of whether they were allowed to or not.

So, yeah, there is the only choice they could make.

The violence just happened.

They've not been able to celebrate Muslims.

They've not been able to celebrate, eat and the Jewish community haven't been able to celebrate either.

So I just don't really think it's very fair.

I think it will create more cov cases.

The hospitals already, you know, under pressure.

I don't see why they should be put under it anymore just by letting us have that week of Christmas.

Detailed guidance for Scotland and Wales will be issued on Thursday.

But the broad message is.

Take care.

We're asking people to keep well within these limits because there is a risk thio households coming together and therefore, if you feel you can get through this Christmas without seeing other people, or if you can see people for one day and no across five days, then try to limit your interaction.

This is not an instruction to travel.

It's not instruction to meet with other people.

People should still use a sense of responsibility, should still ask themselves whether what they are doing is keeping themselves and other people safe.

Northern Ireland has been given a slightly longer window from the 22nd to the 28th of December to allow time to travel between the nation's way recognize the.

For a lot of people, this is an oasis, if you like, that is coming up and they're looking forward to it on.

Of course, it is good to get together.

For many people who have suffered from mental health issues over the year, we feel isolated during this time.

The plans mean people can get together in a bigger group for a few days, but there will still be limits.

You could gather in a private home or a place of worship, but most people still won't be able to go to the pub or to a restaurant together.

There is no flexibility in other areas.

Children whose parents are separated will be able to see both of them over the festive period on.

Then there's the question off enforcement.

At times, the police have been accused of being heavy handed, but they're playing down the chances of penalty fines while the crackers air being pulled.

I will not be task in my office is to be knocking on people's doors on Christmas Day and interrupting the turkey because people may or may not breach it.

I'm sure that's what's behind the government thinking, so we'll see what the rules and regulations come out, but we will continue to place it in a very pragmatic way.

Christmas Day or not, many will seize the opportunity to celebrate Christmas with others.

But political leaders across the UK are urging caution.

Vicky Young, BBC News, Westminster.

So what are the risks of a relaxing the restrictions?

The government scientific advisers are warning that transmission off the virus is most likely when people meet indoors are science editor David Shipman has been looking at the latest research.

It's traditionally the time of year for celebrations.

But when friends and family crowd together and maybe relax about covert for a while, the coronavirus can easily spread on.

Scientists say that scenes like this can lead to infections.

The way that we would normally experience Christmas Christmas meal, for example, with our friends and families is probably the worst possible scenario for this type of virus is going to be difficult to physically distance people care for each other.

They're not used to that.

If you're out of doors away, the evidence suggests you're very unlikely to catch the virus because it gets dispersed in the open air.

But at this time of year, no one wants to spend too long out in the cold.

This is, after all, the season for gatherings indoors, but that brings ah, whole Siris of risks.

In any group sitting down to a meal, it's possible someone may be infected without realizing because they have no symptoms, and the more people there are, the greater that danger, especially if they've come from different households.

One risk is from sharing because dishes or bottles could be contaminated as their passed around.

Another is that if someone is infected, they'll release the virus.

Is they talk on MAWR emerges, the louder people are as they project their voices hour by hour, the longer everyone's together, the mawr, it can accumulate in the air.

And if the windows are closed against the winter cold, there'll be no fresh air to dilute the virus again, increasing the chances of infection by opening windows regularly throughout the day, you can remove the infected particles, so the government's advice is toe open windows, which might make the room colder but should clear the tiny virus particles known as aerosols.

Hands face space.

There is growing evidence that if you are in a poorly ventilated space for a long period of time with people who were infected, that you may be breathing in those aerosols.

And that might be one of the routes infection on, especially in a social setting where the chances are you're not wearing a face covering.

So the guidance is to reduce the numbers getting together and maybe save a big gathering for the summer.

Avoid sharing plates and utensils.

The American government says everyone should bring their own and keep the event as short as possible.

But even with measures like this, the elderly and other vulnerable people may still be a risk.

The virus doesn't know it's Christmas.

It doesn't know it's the after 10 o'clock at night.

It doesn't know whether it's in a pub or in your house.

It is just a virus, and it will.

It thrives on human contact, So there's a Christmas balance to strike between the chances of infection on the benefits to morale.

On getting that right won't be easy.

David Tuckman, BBC News deputy political editor Vicky Young joins me from Westminster, and that's the point, isn't it?

They're gonna be many who welcomed the new rules, but they will also give a lot of people pause for thought.

The message very much is caution, isn't it?

And it's worth saying this is not a free for all.

It doesn't mean that on Christmas Eve you could meet up with two households on Boxing Day.

Another to those Christmas bubbles have to be fixed over those five days, and the government says it's a proportionate response that it allows people to spend some more time with family and friends without the virus transmitting in any significant way.

But be in no doubt.

Scientists do think there will be a rising cases because of this.

And that's why very much people being urged to use their judgment, the personal judgment that many people have used throughout this pandemic, especially when it comes to the elderly on vulnerable, saying, Just because you can do this, it doesn't mean that you have to and I think it reminded to uh to people, particularly in England, who will find out many of them on Thursday that they will be over Christmas in areas where there are other restrictions going on those tears that area is gonna be put into.

There could well be pubs and restaurants closed in many parts of England as well as the rest of the UK.

I think the idea of big Christmas parties are very much off the agenda, Vickie.

Thank you.

Well, there is more information about the new rules for Christmas and who you're allowed to see and where you're allowed to travel.